1. Field of the Invention
The present invention relates to fluid contamination and more particularly relates to the removal of contaminants from common fluids, including dielectric fluids.
2. Background Art
Contamination in hydraulic and lubrication systems is generally considered to be one of the most prevalent causes of machinery failure and can cost manufacturing facilities millions of dollars each year. Within the various types of contamination common to many complex industrial lubrication systems, varnish contamination is one of the most damaging and costly. Varnish contamination is generally considered to be the by-product of many oil-degradation processes in hydraulic and lubrication systems. The effects of varnish on industrial and manufacturing systems range from the nuisance of minor downtime and routine maintenance to a multi-million dollar catastrophic failure of major capital equipment.
A number of explanations for the observed increase in the occurrence of varnish in lubrication oils have been postulated. Tighter filtration requirements, higher flow rates for lubricating oil, higher operating temperatures within machinery, and the generalized industry migration to Group II bases oil formulations have been offered as potential culprits in the degradation of performance in oil lubrication systems.
Identifying varnish in lubrication systems and getting rid of it are essential to maintaining machinery reliability and overall production in a manufacturing or production environment. As hydraulic and lubrication systems continue to improve, the stress on the lubrication oil increases and requires improved base oils and additives to handle the higher temperatures and loads. Oil manufacturers have responded to this challenge by adopting Group II-finished products with improved additive characteristics. The new Group II lubricating oils show much improved oxidation stability over the older Group I formulated products that have been in place since the mid 1900's. However, now that Group II-based lubricating oils have been used in many hydraulic and lubrication systems for more than 10 years, new challenges are arising regarding sludge, varnish and deposit formations. These contaminants are causing problems with operations and, when left alone, may create significant operational issues in critical bearing and servo applications. These problems may also lead to reduced efficiency and production capability.
Varnish is a high molecular weight substance that is generally insoluble in oil. Varnish is typically found as a thin, insoluble film that is deposited on the metal surfaces of machinery components, such as reservoirs, bearings, and servo-valves. Varnish insolubles are more than 75 percent soft contaminants that are less than 1 micron in size and are not measured by traditional laboratory analysis. These varnish insolubles since they are sub-micron in size cannot be removed with traditional mechanical filters, which are only effective to 3 micron in size. Sub-micron insoluble compounds have polar affinities and, over time, begin to migrate from being suspended in the base oil to bonding on machine surfaces, based on system and oil conditions. Initially, the surfaces start to exhibit a gold or tan color, gradually deepening over time to darker gum-like layers that finally develop into varnish. The chemical composition of these sub-micron insoluble materials may vary from case to case. For example, the composition of a varnish on a gas turbine servo valve may not be the same as a varnish deposit found in a steam turbine oil system. Due to their high purity, insoluble compounds are generally considered to be less stable in Group II, III, and IV based oils.
Varnish formation is an operational and reliability issue that is costing manufacturing facilities millions of dollars in production downtime, equipment failures, and life of lubrication oils. All lubricating oils will create insoluble materials given severe and/or unusual operating conditions. These sub-micron insoluble contamination particles create lubricant imbalance due to factors such as oxidation, cross- and chemical-contamination, micro-dieseling and adiabatic compression. The tendency and speed at which lubricating oils produce these by-products is greatly influenced by the formulation of the product, the stress on the oil, and system contamination levels. Synthetic base stocks are an excellent platform; however, if they are not properly formulated, optimum performance will not be achieved, resulting in increased varnish formation.
The varnish deposits that form on machine surfaces can cause numerous operational issues by interfering with the reliable performance of the fluid and the machine's mechanical movements. They can also contribute to wear and corrosion or simply just cling to surfaces. In severe cases, varnish build-up could prevent hydrodynamic lubrication of a bearing surface, resulting in bearing failure. Other potential problems include:                Restriction and sticking in moving mechanical parts such as servo or directional valves;        Increased component wear due to varnish's propensity to attract dirt and solid particle contaminants;        Loss of heat transfer in heat exchangers due to varnish's insulation effect;        Catalytic deterioration of the lubricant;        Plugging of small oil flow orifices and oil strainers;        Increase of friction, heat and energy because varnish acts as a heat insulator;        Reduction in filter efficiency and potential filter plugging;        Damage to mechanical seals;        Journal-bearing failure; and        Increased maintenance costs due to cleanup and disposal of oil.        
Previously known electrostatic filters, while useful in removing certain types of contaminants, have not been particularly effective in removing varnish from various fluids. For example, U.S. Pat. Nos. 6,129,829, 6,284,118, and 6,576,107 are representative of marginally effective filtration systems and which are incorporated herein by reference. Filter such as these are typically designed to be used for a pre-determined period of time (i.e., after so many hours of operation) and are then discarded and replaced by new filters. Unfortunately, there is no way to tell whether or not the filter is actually spent after the pre-determined period of time has elapsed. Depending on the type and quantity of fluid treated during the life of the filter, the filter may be used for too long of a period of time or disposed of prematurely.
Accordingly, those skilled in the art will recognize that there exists a continuing need to identify and develop alternative filtration systems for the treatment of fluids, such as dielectric fluids, in an efficient and cost effective manner. Without additional improvements in the effectiveness and efficiency in removing unwanted contaminants and varnish from various fluids, the operational aspects of certain types of equipment and machinery will continue to be suboptimal.